1. Field of the Invention
This invention relates to devices and arrangements for detecting air or air bubbles in fluid conducting tubing and in particular in fluid conducting tubing forming part of a fluid flow system utilized for the intravenous supply of fluid to a medical patient.
2. Discussion of Background
Typically transparent walled p.v.c. tubing is employed in systems as last-mentioned because it is hygienic and cheap--it being common practice to change and discard the length of tubing in use frequently.
A known arrangement for use in clinical analysis and capable of detecting air in tubing utilizes a device as illustrated in transverse section in FIG. 1 of the accompanying drawings.
Referring to FIG. 1, the known device includes a body--member 1 having a passage 2 passing therethrough in which may be accommodated a length of transparent walled p.v.c. tubing 3. Passage 2 is open at the top (as viewed) in order that the tubing 3 may readily be slotted into position and of course removed after use. Extending into the body 1 from its base and right-hand side (as viewed) respectively are two circular-cylindrical passages 4 and 5 which are orthogonal to each other and exit via apertures 6, 7 respectively into tubing passage 2.
Located in circular cylindrical passage 4 is an infra-red receiver 8 (a phototransistor) which receives infra-red energy transmitted by an infra-red transmitter 9 (an LED).
In operation the output level of receiver 8 depends upon the nature of the fluid passing through the tubing 3 past receiver 8 and transmitter 9. Different fluids will result in different output levels with a significant change if air is present. For example, in a test a voltmeter 10 connected to the output of a suitable detector circuit 11 was found to indicate 0.1 volts when the fluid passing through tubing 3 was distilled water; 0.2 volts when the fluid was semi-skimmed milk; 1.4 volts when the fluid was a 20% intralipid solution and 4.2 volts when air passed through.
Whilst not a primary function of a clinical analyzer, a device as shown in FIG. 1 will therefore operate as a detector of air passing through tubing 3. However, as is represented, p.v.c. tubing typically used in a clinical analyzer is small bore thick-walled tubing with an outside diameter of 2.5 mm and an inside diameter of 0.9 mm. In the intravenous supply of fluids to a patient however the standard p.v.c. tubing used is of relatively large bore and thin walled having an outside diameter of 4 mm and an inside diameter of 3.1 mm.